4702 W GLENHAVEN DR 2020-06-16 - Laserfiche WebLink

Oskar Property Deck Limited CAO,Everett,WA Materials Testing&Consulting,Inc. July 17,2019 19B182 Drainage sources should be tightlined from their collection to the system connection point, or to an appropriately sized catch basin structure located within the site building vicinity and tightlined collectively. If necessary, a pump system can be designed and utilized to transmit stormwater from the back of the site at a lower elevation to the frontage for disposal. All drainage tightlines shall be composed of appropriately sturdy material (such as rigid PVC), sized adequately according to anticipated volume, and anchored or buried sufficiently for protection. MTC recommends all above-grade tightlines traversing slopes or slope-proximal areas be inspected by the property owner periodically to look for signs of damage or displacement that could result in leakage or catastrophic failure and subsequent slope erosion or failure, and be re-anchored or replaced if required. These recommendations are given from a geotechnical and critical area protection standpoint. In the event that the above conflicts with local jurisdiction guidelines and regulations, MTC recommends that we be contacted for additional consultation to determine a most suitable course of action. Standard Erosion Protection Erosion is one of the most common driving forces leading to slope instability. In addition to the above commentary, the following general recommendations should be implemented in general to reduce long- term erosion potential at the project site: 1. The ground surface adjacent to the house should be sloped to drain away at a 5% minimum to prevent ponding of water adjacent to the house. Footing drains and surface gradients should be incorporated as needed for the building and site design to help maintain a dry building and adjacent site area. 2. Minimize the volume and velocity of water that travels toward and down the slope face (via proper choice of site development features including stormwater controls discussed herein). 3. Avoid further accelerating slope erosion and mass wasting due to human activity such as: a) Adding side-cast debris to the slopes during or after construction b) Using heavy construction equipment on or near steep slopes c) Excavating on or near adjacent slope face outside of approved locations d) Placing additional tailings or soils near the slope crest or on the face 4. Construction equipment, construction materials, and native and imported soils should not be placed behind the erosion control devices. Suitable temporary erosion and sediment control measures should be implemented and maintained as needed at the construction site during and immediately after any ground disturbance occurs. Temporary areas bare of vegetation should be protected from erosion via a blanket of straw or rolled erosion control product (RECP) during prolonged breaks in site work and prior to reseeding or revegetation. 5. At the end of the project, all disturbed vegetation should be repaired and maintained until it is established. Concentrated surface water should not be allowed to traverse the slope during or after the construction phase of the project. Recommendations for long-term site drainage controls should be followed as discussed above. Footing drains should be routed into closed pipes and 10 % a